CHAP. xin. RE-ELEVATION OP SCOTLAND. 247 



Others have been left strewed over the bottom of the large 

 intei'vening vale of Strathmore.* 



It may be argued that the transi^ortation of such blocks 

 may have been due not to floating ice, but to a period when 

 Strathmore was filled up with land-ice, a current of which ex- 

 tended from the Perthshire Highlands to the summit of the 

 Sidlaw Hills, and the total absence of marine or fresh-water 

 shells from all deposits, stratified or unstratified, which have 

 any connection with these erratics in Forfarshire and Perth- 

 shire may be thought to favor such a theory. 



But the same mode of transport can scarcely be imagined 

 for those fragments of mica-schist, one of them weighing from 

 eight to ten tons, which were observed much farther south 

 by Mr. Maclaren on the Pentland Hills, near Edinburgh, at 

 the height of 1100 feet above the sea, the nearest mountain 

 composed of this formation being fifty miles distant. f On 

 the same hills, also, at all elevations, stratified gravels occur 

 which, although devoid of shells, it seems hardly possible to 

 refer to any but a marine origin. "f" 



Although I am willing, therefore, to concede that the 

 glaciation of the Scotch mountains, at elevations exceeding 

 2000 feet, may be explained by land-ice, it seems difficult 

 not to embrace the conclusion that a subsidence took place 

 not merely of 500 or 600 feet, as demonstrated by the 

 marine shells, but to a much greater amount, as shown by the 

 present position of erratics and some 2Datches of stratified 

 drift. The absence of marine shells at greater heights than 

 525 feet above the sea will be treated of in a future chapter. 

 It may in part, perhaps, be ascribed to the action of glaciers, 

 which swept out marine strata from all the higher valleys, 

 after the re-emergence of the land. 



* Proceedings of the Geological So- f Maclaren, Geology of Fife, &o., 



ciety, vol. iii. p. 3M. p. 220. 



17 



